I have created a small-ish ecore diagram model. It's from a C++ program, and I'm creating it by hand, so (1) the ecore diagram is not really powerful enough to model C++ templates well enough, and (2) I don't want to recreate it manually. So, I'd like to convert it to UML. The only advice I can find with Google-fu is to use the UML2 editor, but I can't see how to install that in Eclipse Juno, and in any case, it seems as if it's been superceded by Papyrus. But I also can't seem to find a way to import an ECore model into Papyrus, so I'm stumped.

Is this sensible? Am I looking to so the right thing? Should I start over, and consign the week or so I spent creating the Ecore model to learning?

You can use the UML exporter of EMF.
First, create a .genmodel file for your .ecore file. (New > Other > EMF Generator Model).
Open this .genmodel file with the specialized editor.
Right-click on the root package and choose "Export Model..." > UML Model.

This will get you an equivalent uml model for which you can assoicate a Papyrus diagram file.

So, I can't figure out the next part. I want to load my generated uml files into the Papyrus editor. All the tutorials and documents I have seen are out of date. The menu entries in the documentation just don't seem to exist.

This is all very frustrating. It doesn't seem like this should be so hard. How does anybody get the stuff to work without days and days of struggling? I mean, a plausible competitor to MDSE is just typing in Emacs. If this stuff always requires weeks of effort to get the tools configured and working, installing multiple undocumented Eclipse plug-ins and tracking things down on forums, it's hard to see how MDSE in this way is really a competitor.